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A snippet of Java code with keywords highlighted in blue and bold font. In the Java programming language, a keyword is any one of 68 reserved words [1] that have a predefined meaning in the language. Because of this, programmers cannot use keywords in some contexts, such as names for variables, methods, classes, or as any other identifier. [2]
longer identifiers may be disfavored because of visual clutter; It is an open research issue whether some programmers prefer shorter identifiers because they are easier to type, or think up, than longer identifiers, or because in many situations a longer identifier simply clutters the visible code and provides no perceived additional benefit.
An identifier is the name of an element in the code. There are certain standard naming conventions to follow when selecting names for elements. Identifiers in Java are case-sensitive. An identifier can contain: Any Unicode character that is a letter (including numeric letters like Roman numerals) or digit. Currency sign (such as ¥).
Which character sequences constitute identifiers depends on the lexical grammar of the language. A common rule is alphanumeric sequences, with underscore also allowed (in some languages, _ is not allowed), and with the condition that it can not begin with a numerical digit (to simplify lexing by avoiding confusing with integer literals) – so foo, foo1, foo_bar, _foo are allowed, but 1foo is ...
If a variable is only referenced by a single identifier, that identifier can simply be called the name of the variable; otherwise, we can speak of it as one of the names of the variable. For instance, in the previous example the identifier "total_count" is the name of the variable in question, and "r" is another name of the same variable.
Identifiers in Fortran 90 modules must be further mangled, because the same procedure name may occur in different modules. Since the Fortran 2003 Standard requires that module procedure names not conflict with other external symbols, [8] compilers tend to use the module name and the procedure name, with a distinct marker in between. For example:
In Java, ActionScript, [5] and other object-oriented languages the use of the dot is known as "dot syntax". [6] Other examples include: As an example of a relational database, in Microsoft SQL Server the fully qualified name of an object is the one that specifies all four parts: server_name.[database_name].[schema_name].object_name. [7]
Formally this means that it satisfies the usual lexical syntax (syntax of words) of identifiers – for example, being a sequence of letters – but cannot be used where identifiers are used. For example, the word if is commonly a reserved word, while x generally is not, so x = 1 is a valid assignment, but if = 1 is not.